BigDecimal#sqrt precision too high

[tompng]

x = BigDecimal('1.'+'1'*1000)
x.precision #=> 1001
x.sqrt(200).precision #=> expected: 200+extra, actual: 1126

Actual problem

x=BigDecimal('3.14')
100.times{
  x = x.sqrt(200)
  p x.precision
}

# Expect output
208
213
209
210
208
209
...(completes in about 0.03s)

# Actual output
208
226
253
289
...
9504
10567
11736
...(does not end)

Workaround
x.sqrt(prec).mult(1, prec)